TCP/IP Transport Layer Protocols

Transmission Control Protocol (TCP) is a reliable, connection-oriented, protocol that uses sequence and acknowledgement numbers to provide reliability. TCP verifies that the remote end is listening prior to sending data, using a 3-way handshake: SYN, SYN/ACK, ACK.

User Datagram Protocol (UDP) is a best-effort, connectionless, protocol that does not have sequence or acknowledgement numbers, and does not do far-end verification.